It's a multiply deficiency Symptome.
And for sure, I see symtpomes of Zinc, Iron, Manganese and Nitrogen missing.
Look:


Look very similiar, but was found in spring after a long, long winter in the greenhouse. Was identified as an winter chlorosis, so insufficient root activitiy was the cause of the symptome.

In your case you should see, if the roots are in a proper function, to take up enough nutrients... also the much water will wash out nutrients quite good, as the high phosphorus content in the fertilizer blocks many micronutients in the fertilizer being taken u by the roots.
So the high phosphor content supports those symptomes...
So I guess: Improper root function due weather and climatic influences (maybe a slight root damage due to much water) and micronutrient blockade in the soil by to high phosphor contents in the fertilizer

*smile* That's what I tought, but it isn't!

This is a winter chlorosis, because with less root activity roots cannot uptake micronutrients and the transportation within the plant is somewhat limited, thus a mild chlorosis up to a severe complete yellowing of the entire leaf is shown.


Okay?

This is iron deficiency:
Typical:


Severe:


See the difference, because in iron, usually the leaf blade fades in green coloration, even the carotinoide yellow color fades. So the leaf blades becomes pale green and whitens up more and more, but the veins remain still green and a clear and sharp, like painted on the leaf with the finest and best stylograph.
In severe symptoms the leaves will brighten up to nearly complete white, so the last picture shows this symptom, also here the veins cleared and are white now...
I think the difference is clear.

I encounter also such symptoms, if some rootstocks are stresses by high daytime temperatures folloed by cold night temperatures, were the container won't heat up that fast as the air or the leaves of the canopy.
So my clemetine on Macrophylla stock shows such symptoms, to a limited extent, but visibly... Fertilisation and soil pH are not the problem, it's simply the climatic effect and will go away if the temperatures will get more stable and constant, without such abrupt changes...

I always recognized iron chlorosis from this: http://www.citrusplants.com/fertilizer.htm
So to me it looks identical to:

Sorry, that the picture isn't larger, but I have certain other pictures of those leaves and certain other plants visited... Usure, I send the picture to an expert, who said it's a typical symptom of Nutrient uptake problems, and named it winter chlorosis.

And today I am sure, that those plants can't suffer form iron chlorosis, because having an acid potting mixture and a good fertilizer, so iron would be good available. So I start understand, why iron chlorosis may develop and why not.
And often what people claim iron chlorosis is far from truth. So in the picture


This is not iron chlorosis, it look somewhat similiar, but it is not.
Because I made the picture, I can be sure.
This is why I looked at your picture and think: It's not iron chlorosis...
That's what I think.... but I cannot be sure, because it's not my picture, not my plant.

so it's your decision:
Try to cure an iron deficiency, or cure an winter chlorosis...

I just wanted to add a additional guess or possibility for those leaf symtom

Which nutrient is in deficiency on this citrus? Iron or managanese?